Download File - Ms. Perez`s Science

CELLS UNIT
A Tour of the Cell 2
Concept 6.5: Mitochondria and
chloroplasts change energy from one
form to another
■ Mitochondria are the sites of cellular respiration, a metabolic process that
generates ATP
■ Chloroplasts, found in plants and algae, are the sites of photosynthesis
■ Peroxisomes are oxidative organelles
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
■ Mitochondria and chloroplasts
– Are not part of the endomembrane system
– Have a double membrane
– Have proteins made by free ribosomes
– Contain their own DNA
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Mitochondria: Chemical Energy
Conversion
■ Mitochondria are in nearly all eukaryotic cells
■ They have a smooth outer membrane and an inner membrane folded into
cristae
■ The inner membrane creates two compartments: intermembrane space
and mitochondrial matrix
■ Some metabolic steps of cellular respiration are catalyzed in the
mitochondrial matrix
■ Cristae present a large surface area for enzymes that synthesize ATP
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-17
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
0.1 µm
Chloroplasts: Capture of Light Energy
■ The chloroplast is a member of a family of organelles called plastids
■ Chloroplasts contain the green pigment chlorophyll, as well as enzymes
and other molecules that function in photosynthesis
■ Chloroplasts are found in leaves and other green organs of plants and in
algae
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
■ Chloroplast structure includes:
– Thylakoids, membranous sacs, stacked to form a granum
– Stroma, the internal fluid
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-18
Ribosomes
Stroma
Inner and outer
membranes
Granum
Thylakoid
1 µm
Peroxisomes: Oxidation
■ Peroxisomes are specialized metabolic compartments bounded by a
single membrane
■ Peroxisomes produce hydrogen peroxide and convert it to water
■ Oxygen is used to break down different types of molecules
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-19
Chloroplast
Peroxisome
Mitochondrion
1 µm
Concept 6.6: The cytoskeleton is a
network of fibers that organizes
structures and activities in the cell
■ The cytoskeleton is a network of fibers extending throughout the
cytoplasm
■ It organizes the cell’s structures and activities, anchoring many
organelles
■ It is composed of three types of molecular structures:
– Microtubules
– Microfilaments
– Intermediate filaments
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-20
Microtubule
0.25 µm
Microfilaments
Roles of the Cytoskeleton: Support,
Motility, and Regulation
■ The cytoskeleton helps to support the cell and maintain its shape
■ It interacts with motor proteins to produce motility
■ Inside the cell, vesicles can travel along “monorails” provided by the
cytoskeleton
■ Recent evidence suggests that the cytoskeleton may help regulate
biochemical activities
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-21
ATP
Vesicle
Receptor for
motor protein
Motor protein Microtubule
(ATP powered) of cytoskeleton
(a)
Microtubule
(b)
Vesicles
0.25 µm
Components of the Cytoskeleton
■ Three main types of fibers make up the cytoskeleton:
– Microtubules are the thickest of the three components of the
cytoskeleton
– Microfilaments, also called actin filaments, are the thinnest
components
– Intermediate filaments are fibers with diameters in a middle range
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Table 6-1
10 µm
10 µm
10 µm
Column of tubulin dimers
Keratin proteins
Actin subunit
Fibrous subunit (keratins
coiled together)
25 nm
7 nm


Tubulin dimer
8–12 nm
Table 6-1a
10 µm
Column of tubulin dimers
25 nm


Tubulin dimer
Table 6-1b
10 µm
Actin subunit
7 nm
Table 6-1c
5 µm
Keratin proteins
Fibrous subunit (keratins
coiled together)
8–12 nm
Microtubules
■ Microtubules are hollow rods about 25 nm in diameter and about 200 nm
to 25 microns long
■ Functions of microtubules:
– Shaping the cell
– Guiding movement of organelles
– Separating chromosomes during cell division
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Centrosomes and Centrioles
■ In many cells, microtubules grow out from a centrosome near the nucleus
■ The centrosome is a “microtubule-organizing center”
■ In animal cells, the centrosome has a pair of centrioles, each with nine
triplets of microtubules arranged in a ring
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-22
Centrosome
Microtubule
Centrioles
0.25 µm
Longitudinal section Microtubules Cross section
of one centriole
of the other centriole
Cilia and Flagella
■ Microtubules control the beating of cilia and flagella, locomotor
appendages of some cells
■ Cilia and flagella differ in their beating patterns
Video: Chlamydomonas
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Video: Paramecium Cilia
Fig. 6-23
Direction of swimming
(a) Motion of flagella
5 µm
Direction of organism’s movement
Power stroke Recovery stroke
(b) Motion of cilia
15 µm
■ Cilia and flagella share a common ultrastructure:
– A core of microtubules sheathed by the plasma membrane
– A basal body that anchors the cilium or flagellum
– A motor protein called dynein, which drives the bending movements
of a cilium or flagellum
Animation: Cilia and Flagella
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-24
Outer microtubule
doublet
0.1 µm
Dynein proteins
Central
microtubule
Radial
spoke
Protein crosslinking outer
doublets
Microtubules
Plasma
membrane
(b) Cross section of
cilium
Basal body
0.5 µm
(a) Longitudinal
section of cilium
0.1 µm
Triplet
(c) Cross section of basal body
Plasma
membrane
■ How dynein “walking” moves flagella and cilia:
− Dynein arms alternately grab, move, and release the outer
microtubules
– Protein cross-links limit sliding
– Forces exerted by dynein arms cause doublets to curve, bending the
cilium or flagellum
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-25
Microtubule
doublets
ATP
Dynein
protein
(a) Effect of unrestrained dynein movement
ATP
Cross-linking proteins
inside outer doublets
Anchorage
in cell
(b) Effect of cross-linking proteins
1
3
2
(c) Wavelike motion
Fig. 6-25a
Microtubule
doublets
ATP
Dynein
protein
(a) Effect of unrestrained dynein movement
Fig. 6-25b
ATP
Cross-linking proteins
inside outer doublets
Anchorage
in cell
(b) Effect of cross-linking proteins
1
3
2
(c) Wavelike motion
Microfilaments (Actin Filaments)
■ Microfilaments are solid rods about 7 nm in diameter, built as a twisted
double chain of actin subunits
■ The structural role of microfilaments is to bear tension, resisting pulling
forces within the cell
■ They form a 3-D network called the cortex just inside the plasma
membrane to help support the cell’s shape
■ Bundles of microfilaments make up the core of microvilli of intestinal cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-26
Microvillus
Plasma membrane
Microfilaments (actin
filaments)
Intermediate filaments
0.25 µm
■ Microfilaments that function in cellular motility contain the protein myosin
in addition to actin
■ In muscle cells, thousands of actin filaments are arranged parallel to one
another
■ Thicker filaments composed of myosin interdigitate with the thinner actin
fibers
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-27
Muscle cell
Actin filament
Myosin filament
Myosin arm
(a) Myosin motors in muscle cell contraction
Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
(b) Amoeboid movement
Nonmoving cortical
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Vacuole
Parallel actin
filaments
(c) Cytoplasmic streaming in plant cells
Cell wall
Fig, 6-27a
Muscle cell
Actin filament
Myosin filament
Myosin arm
(a) Myosin motors in muscle cell contraction
Fig. 6-27bc
Cortex (outer cytoplasm):
gel with actin network
Inner cytoplasm: sol
with actin subunits
Extending
pseudopodium
(b) Amoeboid movement
Nonmoving cortical
cytoplasm (gel)
Chloroplast
Streaming
cytoplasm
(sol)
Vacuole
Parallel actin
filaments
(c) Cytoplasmic streaming in plant cells
Cell wall
•
Localized contraction brought about by actin and myosin also drives
amoeboid movement
•
Pseudopodia (cellular extensions) extend and contract through the
reversible assembly and contraction of actin subunits into microfilaments
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
■ Cytoplasmic streaming is a circular flow of cytoplasm within cells
■ This streaming speeds distribution of materials within the cell
■ In plant cells, actin-myosin interactions and sol-gel transformations drive
cytoplasmic streaming
Video: Cytoplasmic Streaming
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Intermediate Filaments
■ Intermediate filaments range in diameter from 8–12 nanometers, larger
than microfilaments but smaller than microtubules
■ They support cell shape and fix organelles in place
■ Intermediate filaments are more permanent cytoskeleton fixtures than the
other two classes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Concept 6.7: Extracellular components
and connections between cells help
coordinate cellular activities
■ Most cells synthesize and secrete materials that are external to the
plasma membrane
■ These extracellular structures include:
– Cell walls of plants
– The extracellular matrix (ECM) of animal cells
– Intercellular junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cell Walls of Plants
■ The cell wall is an extracellular structure that distinguishes plant cells from
animal cells
■ Prokaryotes, fungi, and some protists also have cell walls
■ The cell wall protects the plant cell, maintains its shape, and prevents
excessive uptake of water
■ Plant cell walls are made of cellulose fibers embedded in other
polysaccharides and protein
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
■ Plant cell walls may have multiple layers:
– Primary cell wall: relatively thin and flexible
– Middle lamella: thin layer between primary walls of adjacent cells
– Secondary cell wall (in some cells): added between the plasma
membrane and the primary cell wall
•
Plasmodesmata are channels between adjacent plant cells
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-28
Secondary
cell wall
Primary
cell wall
Middle
lamella
1 µm
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
Plasmodesmata
Fig. 6-29
RESULTS
10 µm
Distribution of cellulose
synthase over time
Distribution of microtubules
over time
The Extracellular Matrix (ECM) of
Animal Cells
■ Animal cells lack cell walls but are covered by an elaborate extracellular
matrix (ECM)
■ The ECM is made up of glycoproteins such as collagen, proteoglycans, and
fibronectin
■ ECM proteins bind to receptor proteins in the plasma membrane called
integrins
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-30
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Polysaccharide
molecule
Carbohydrates
Fibronectin
Core
protein
Integrins
Proteoglycan
molecule
Plasma
membrane
Proteoglycan complex
Microfilaments
CYTOPLASM
Fig. 6-30a
Collagen
Proteoglycan
complex
EXTRACELLULAR FLUID
Fibronectin
Integrins
Plasma
membrane
Microfilaments
CYTOPLASM
Fig. 6-30b
Polysaccharide
molecule
Carbohydrates
Core
protein
Proteoglycan
molecule
Proteoglycan complex
■ Functions of the ECM:
– Support
– Adhesion
– Movement
– Regulation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Intercellular Junctions
■ Neighboring cells in tissues, organs, or organ
systems often adhere, interact, and communicate
through direct physical contact
■ Intercellular junctions facilitate this contact
■ There are several types of intercellular junctions
–
–
–
–
Plasmodesmata
Tight junctions
Desmosomes
Gap junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Plasmodesmata in Plant Cells
■ Plasmodesmata are channels that perforate plant cell walls
■ Through plasmodesmata, water and small solutes (and sometimes
proteins and RNA) can pass from cell to cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-31
Cell walls
Interior
of cell
Interior
of cell
0.5 µm
Plasmodesmata Plasma membranes
Tight Junctions, Desmosomes, and
Gap Junctions in Animal Cells
■ At tight junctions, membranes of neighboring cells
are pressed together, preventing leakage of
extracellular fluid
■ Desmosomes (anchoring junctions) fasten cells
together into strong sheets
■ Gap junctions (communicating junctions) provide
cytoplasmic channels between adjacent cells
Animation: Tight Junctions
Animation: Desmosomes
Animation: Gap Junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-32
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
Tight junction
Intermediate
filaments
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Desmosome
1 µm
Extracellular
matrix
Gap junction
0.1 µm
Fig. 6-32a
Tight junctions prevent
fluid from moving
across a layer of cells
Tight junction
Intermediate
filaments
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Extracellular
matrix
Plasmodesmata in Plant Cells
■ Plasmodesmata are channels that perforate plant cell walls
■ Through plasmodesmata, water and small solutes (and sometimes
proteins and RNA) can pass from cell to cell
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-31
Cell walls
Interior
of cell
Interior
of cell
0.5 µm
Plasmodesmata Plasma membranes
Tight Junctions, Desmosomes, and
Gap Junctions in Animal Cells
■ At tight junctions, membranes of neighboring cells
are pressed together, preventing leakage of
extracellular fluid
■ Desmosomes (anchoring junctions) fasten cells
together into strong sheets
■ Gap junctions (communicating junctions) provide
cytoplasmic channels between adjacent cells
Animation: Tight Junctions
Animation: Desmosomes
Animation: Gap Junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 6-32
Tight junction
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
Tight junction
Intermediate
filaments
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Desmosome
1 µm
Extracellular
matrix
Gap junction
0.1 µm
Fig. 6-32a
Tight junctions prevent
fluid from moving
across a layer of cells
Tight junction
Intermediate
filaments
Desmosome
Gap
junctions
Space
between
cells
Plasma membranes
of adjacent cells
Extracellular
matrix
Fig. 6-UN1
Cell Component
Concept 6.3
The eukaryotic cell’s genetic
instructions are housed in
the nucleus and carried out
by the ribosomes
Structure
Surrounded by nuclear
envelope (double membrane)
perforated by nuclear pores.
The nuclear envelope is
continuous with the
endoplasmic reticulum (ER).
Nucleus
Function
Houses chromosomes, made of
chromatin (DNA, the genetic
material, and proteins); contains
nucleoli, where ribosomal
subunits are made. Pores
regulate entry and exit of
materials.
(ER)
Two subunits made of riboProtein synthesis
somal RNA and proteins; can be
free in cytosol or bound to ER
Ribosome
Concept 6.4
The endomembrane system
regulates protein traffic and
performs metabolic functions
in the cell
Concept 6.5
Mitochondria and chloroplasts change energy from
one form to another
Extensive network of
membrane-bound tubules and
sacs; membrane separates
lumen from cytosol;
continuous with
the nuclear envelope.
Smooth ER: synthesis of
lipids, metabolism of carbohydrates, Ca2+ storage, detoxification of drugs and poisons
Golgi apparatus
Stacks of flattened
membranous
sacs; has polarity
(cis and trans
faces)
Modification of proteins, carbohydrates on proteins, and phospholipids; synthesis of many
polysaccharides; sorting of Golgi
products, which are then
released in vesicles.
Lysosome
Membranous sac of hydrolytic
enzymes (in animal cells)
Vacuole
Large membrane-bounded
vesicle in plants
Digestion, storage, waste
disposal, water balance, cell
growth, and protection
Mitochondrion
Bounded by double
membrane;
inner membrane has
infoldings (cristae)
Cellular respiration
Endoplasmic reticulum
(Nuclear
envelope)
Chloroplast
Peroxisome
Rough ER: Aids in synthesis of
secretory and other proteins from
bound ribosomes; adds
carbohydrates to glycoproteins;
produces new membrane
Breakdown of ingested substances,
cell macromolecules, and damaged
organelles for recycling
Typically two membranes
Photosynthesis
around fluid stroma, which
contains membranous thylakoids
stacked into grana (in plants)
Specialized metabolic
compartment bounded by a
single membrane
Contains enzymes that transfer
hydrogen to water, producing
hydrogen peroxide (H2O2) as a
by-product, which is converted
to water by other enzymes
in the peroxisome
Fig. 6-UN1a
Structure
Cell Component
Concept 6.3
The eukaryotic cell’s genetic
instructions are housed in
the nucleus and carried out
by the ribosomes
Nucleus
Function
Surrounded by nuclear
envelope (double membrane)
perforated by nuclear pores.
The nuclear envelope is
continuous with the
endoplasmic reticulum (ER).
Houses chromosomes, made of
chromatin (DNA, the genetic
material, and proteins); contains
nucleoli, where ribosomal
subunits are made. Pores
regulate entry and exit os
materials.
Two subunits made of ribosomal RNA and proteins; can be
free in cytosol or bound to ER
Protein synthesis
(ER)
Ribosome
Fig. 6-UN1b
Cell Component
Concept 6.4
Endoplasmic reticulum
The endomembrane system
(Nuclear
regulates protein traffic and
envelope)
performs metabolic functions
in the cell
Golgi apparatus
Lysosome
Vacuole
Structure
Function
Extensive network of
membrane-bound tubules and
sacs; membrane separates
lumen from cytosol;
continuous with
the nuclear envelope.
Smooth ER: synthesis of
lipids, metabolism of carbohydrates, Ca2+ storage, detoxification of drugs and poisons
Stacks of flattened
membranous
sacs; has polarity
(cis and trans
faces)
Rough ER: Aids in sythesis of
secretory and other proteins
from bound ribosomes; adds
carbohydrates to glycoproteins;
produces new membrane
Modification of proteins, carbohydrates on proteins, and phospholipids; synthesis of many
polysaccharides; sorting of
Golgi products, which are then
released in vesicles.
Breakdown of ingested subMembranous sac of hydrolytic stances cell macromolecules,
enzymes (in animal cells)
and damaged organelles for
recycling
Large membrane-bounded
vesicle in plants
Digestion, storage, waste
disposal, water balance, cell
growth, and protection
Fig. 6-UN1c
Cell Component
Concept 6.5
Mitochondrion
Mitochondria and chloroplasts change energy from
one form to another
Structure
Bounded by double
membrane;
inner membrane has
infoldings (cristae)
Function
Cellular respiration
Chloroplast
Typically two membranes
around fluid stroma, which
contains membranous thylakoids
stacked into grana (in plants)
Photosynthesis
Peroxisome
Specialized metabolic
compartment bounded by a
single membrane
Contains enzymes that transfer
hydrogen to water, producing
hydrogen peroxide (H2O2) as a
by-product, which is converted
to water by other enzymes
in the peroxisome
Fig. 6-UN2
Fig. 6-UN3
You should now be able to:
1.
Distinguish between the following pairs of terms: magnification and
resolution; prokaryotic and eukaryotic cell; free and bound ribosomes;
smooth and rough ER
2.
Describe the structure and function of the components of the
endomembrane system
3.
Briefly explain the role of mitochondria, chloroplasts, and peroxisomes
4.
Describe the functions of the cytoskeleton
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
5.
Compare the structure and functions of microtubules, microfilaments,
and intermediate filaments
6.
Explain how the ultrastructure of cilia and flagella relate to their
functions
7.
Describe the structure of a plant cell wall
8.
Describe the structure and roles of the extracellular matrix in animal
cells
9.
Describe four different intercellular junctions
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings